Generalized Drell-Hearn-Gerasimov sum rule at order O(p4) in chiral perturbation theory

We calculate the forward spin-dependent photon-nucleon Compton amplitudes S1 and S2 as functions of photon energy ν and mass Q2 at the next-to-leading (O(p4)) order in chiral perturbation theory, from which we extract the contribution to a generalized Drell-Hearn-Gerasimov sum rule at low Q2. The result indicates a much rapid Q2 variation of the sum rule than a simple dimensional analysis would yield.